Reduced effectiveness of pesticides: Just as some populations of mosquitoes developed resistance to the now-
banned pesticide DDT, many people are concerned that insects will become resistant to B.t. or other crops that
have been genetically-modified to produce their own pesticides.
Gene transfer to non-target species Another concern is that crop plants engineered for herbicide tolerance and
weeds will cross-breed, resulting in the transfer of the herbicide resistance genes from the crops into the weeds.
These "superweeds" would then be herbicide tolerant as well. Other introduced genes may cross over into non-
modified crops planted next to GM crops.
There are several possible solutions to the three problems mentioned above. Genes are exchanged
between plants via pollen. Two ways to ensure that non-target species will not receive introduced genes from
GM plants are to create GM plants that are male sterile (do not produce pollen) or to modify the GM plant so
that the pollen does not contain the introduced gene. Cross-pollination would not occur, and if harmless insects
such as monarch caterpillars were to eat pollen from GM plants, the caterpillars would survive.
Another possible solution is to create buffer zones around fields of GM crops. For example, non-GM
corn would be planted to surround a field of B.t. GM corn, and the non-GM corn would not be harvested.
Beneficial or harmless insects would have a refuge in the non-GM corn, and insect pests could be allowed to
destroy the non-GM corn and would not develop resistance to B.t. pesticides. Gene transfer to weeds and other
crops would not occur because the wind-blown pollen would not travel beyond the buffer zone .Estimates of the
necessary width of buffer zones range from 6 meters to 30 meters or more. This planting method may not be
feasible if too much acreage is required for the buffer zones.
(2). Human health risks Allergenicity: Many children in the U.S and Europe have developed life-threatening allergies to peanuts and
other foods. There is a possibility that introducing a gene into a plant may create a new allergen or cause an
allergic reaction in susceptible individuals. A proposal to incorporate a gene from Brazil nuts into soybeans was
abandoned because of the fear of causing unexpected allergic reaction.